In DE 697 13 645 T2, a device for cooling the interior of a hollow profile, in this case a plastic pipe, by means of cooling air is described. For this purpose, a hollow cylinder that is closed at the front is pushed into the hollow mandrel of an extruder head and protrudes into the following calibrating unit, an annular gap remaining between the outer wall of the hollow cylinder and the inner wall of the extruded pipe. The hollow cylinder is double-walled and is supplied with cooling water through a central feed line, which opens out into the front end wall of the hollow cylinder. This cooling water flows from its inlet point in the front end wall of the hollow cylinder radially outwards and then back through the cylindrical double casing to the extruder head. In the region of the mandrel, the double casing is bent conically inwards and comes to lie against the circumference of the central cooling water feed line. The cooling air is blown into the hollow cylinder in the direction of extrusion and deflected outwards at the cone formed by the double casing onto the wall of the hollow cylinder. Provided there are through-openings, through which the cooling air flows into the annular gap. There it passes over the inner wall of the extruded pipe and cools it down. The heat taken up by the cooling air is removed again, at least partially, by the cooling water flowing in counterflow in the double casing, so that the cooling air can remove heat from the extruded pipe over the entire length of the annular gap.
In U.S. Pat. No. 4,545,751, a device for cooling the interior of a corrugated tubing produced on an extrusion line is described. Screwed as an extension onto the mandrel of the extruder head of this device is a housing, which reaches into a peripheral mould for creating the corrugation of the tubing to be produced. Arranged in the housing is a Ranque vortex chamber, the cooling air outlet of which opens out into the housing. The latter has in turn radial outlet openings, through which the cooling air flows into the extruded hollow strand lying against the mould and cools it from the inside.
For some years, equipment that makes it possible to change the dimensions of an extruded plastic profile while the production process is in progress has been available. This includes calibrating sleeves, the cross section of which can be changed within relatively wide limits and which have an inlet that can is radially adjustable to match the changing cross section. Such a calibrating sleeve is described in DE 10 2005 002 820 B3.
In particular on account of their radial dimensions, the prior-art devices for cooling the interior of extruded hollow strands in a calibrating device described at the beginning cannot be used in calibrating devices designed for making a dimensional change while operation is in progress, in particular in the case of small cross sections of the hollow strands.
This also applies to a device for extruding hollow strands from thermoplastic material that is disclosed in the subsequently published DE 10 2005 031 747 A1. This has, inter alia, an extruder head with a mandrel and also a calibrating device. Formed in the mandrel is a least one Ranque vortex chamber, the cooling air outlet of which leads into the interior space of the extruded hollow profile.